1. Cross-Reference to Related Applications
This application claims priority under 35 U.S.C. §119 from European Patent Application No. 07001847.8, filed Jan. 29, 2007, the entire disclosure of which is hereby incorporated by reference herein.
2. Field of the Invention
The present invention relates generally to emulsions, and more particularly, relates to emulsions used in the production of paper.
3. Background Information
Pitch and stickies are interfering substances in the wet end of paper machines that can affect both machine operation and paper quality. The terms “pitch” or “wood pitch” as used herein refer to a colloidal dispersion of wood-derived hydrophobic particles released from the fibers during a pulping process. Wood pitch includes fatty acids, resin acids, the insoluble salts thereof, and esters of fatty acids with glycerol, sterols, and other fats and waxes. The hydrophobic components of pitch, particularly triglycerides, are considered one of the major factors determining whether the presence of such pitch will lead to deposit problems. Deposit-forming pitch often contains significantly high amounts of triglyciderides. As used herein, “stickies” mean sticky materials and interfering substances that arise from components of recycled fibers, such as adhesives and coatings. Stickies can come from coated broke, recycled waste paper for board making and de-inked pulp (DIP). The stickies from coated broke is sometimes called white pitch. Deposition of pitch and stickies often leads to defects in the finished product, and paper machine downtime, causing lost profits to the mill. These problems become more significant when paper mills “close up” their process water systems for conservation and environmental reasons. Unless the pitch and stickies are continuously removed from the system in a controlled manner, these interfering substances will accumulate and eventually lead to deposition and runnability problems. Technology in place today is based on fixing the pitch or stickies to the fibers before they have a chance to agglomerate, or alternatively, coating the pitch or stickies with a polymer that makes them non-tacky and therefore unable to agglomerate.
Minimizing or preventing the deposit of pitch and stickies in pulp and paper making processes is therefore necessary to minimize equipment fouling and down time, maximizing production efficiency, and improving product quality.
Methods for pitch control include cationic fixation with alum or cationic polymers, dispersion with surfactants, absorption with talc, and chelation of heavy metals. Typically used pitch controls include silicon polyelectrolytes (U.S. Pat. No. 5,527,431), proteins and polymers (U.S. Publication No. 2002/0096293 A1), non-ionic surfactants (International Publication No. WO 2005/019537 A1), and melamine formaldehyde polymers (European Patent Publication No. 0569085 A1). Enzymatic methods also are known. For example, U.S. Pat. No. 5,176,796 (Irie) discloses adding acylglycerol lipase to mechanical pulp paperstock or reused water. Among the various so-called “pitch control” agents, non-ionic surfactants play an important role due to their high biological degradability. Unfortunately, the products do not prevent the formation of agglomerates and their ability to disperse fine particles over a longer time is not always satisfying.
There remains a need for compositions which reduce the formation of pitch and stickies in paper pulp, and an improved pitch control system in the production of paper.